Electron discharge device



M h 4 J.. R. PIERCE ELECTRON DISCHARGE DEVICE Filed Feb. 22, 1945.

u u m M. l G 29 7 I 2 2 F 590 w WM 21? a & V/" 2 A f/7 i a l A flan: WM l Mi w. III W U fi I III/I INVENTOR J. R. P/'RCE ATTORNEY Patented Mar. 4, 1947 2,416,714 ELECTRON DISCHARGE DEVICE John R. Pierce, Millburn, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 22, 1942, Serial No. 476,677

Claims. (01. 25027.5)

This invention relates to electron discharge devices and more particularly to velocity variation oscillators of the reflection type and operable at extremely high frequencies, for example frequencies corresponding to wave-lengths of the I order of one centimeter.

Velocity variation oscillators of the reflection type comprise, in general, a cavity resonator hav- .ing a ap therein, an electron gun for projecting a stream of electrons across this gap whereby the stream is velocity varied in accordance with the radio frequency field extant in the resonator, and a reflecting or repeller electrode efgap in proper phase to contribute energy to the radio frequency field and thus to sustainoscillations'.

The frequency of the oscillations generated depends upon the transit time of the forwardly projected electrons across the gap and, in general, the higher the frequency desired the shorter the transit time required. Also, in generahthe higher the frequency desired, the smaller the physical parameters of the resonator and electrodes must be. In any oscillator of thistype, the operating efiiciency and other characteristics are dependent largely upon the magnitude of the forwardly projected electron current crossing the gap in proportion to the total forwardly projected electron current and the magnitude of the current projected into the gap in the reverse direction. The attainment of desirable operating characteristics in devices wherein the elements are of'the small dimensions requisite for microwave operation entails the device.

Furthermore, in reflection type velocity variation oscillators thecharacter of theelectric field in the region wherein the reversal of electron motion and the driftaction occurs is largely determinative of the electronic conductance which can be realized and of the range of frequenciesthroughout which the device can be tuned electronically, that is by varying the potentialof the reflecting or repeller electrode.

the gap in the cavity resonator.

One object of thisinvention is to enable and to facilitate the attainment and maintenance of extremely accurate location. of the electron gun and repeller electrode with respect to the cavity resonator gap in velocity variation oscillators of the reflection type. V v

Another object of this invention isTto realize in the drift space region of a reflection type velocity variation oscillator a non-uniform electric field of such character as to sharply focus the reflected electrons upon the gap and to assure a strong drift action. V

In accordance with one feature of this invention, the cavity resonator, electron gun and, refleeting or repeller electrode are fabricated as a rigid unitary assembly and are of such construction that they can be coaxially aligned readily, both mechanically and optically, with great accuracy during the fabrication of the unitary as sembly. t

,In accordance with another feature of this invention, the repeller electrode is made in the form of an open-ended cylindrical tube which acts as a converging electron optical mirror effective to focus the reflected electron stream upon In accordance with a further feature of this invention, the, repeller electrode and cavity'res onator are so constructed and arranged that the field in which the drift action occurs decreases in intensity toward the zero equipotential region thereof whereby a strong drift action and a 'rle atively large change in electron transit time through the drift space with relatively small change in the energy of an electron projected into this space are obtained. r

The invention and the above-notedand other features thereof will be understood more clearly and fully from the following detaileddescription with reference to the accompanyingdrawing, in which: I

Fig. 1 is an elevational view in section of a velocity variation reflection type oscillator illustrative of one embodiment of this invention; and Fig. 2 is a diagram, to a greatly enlarged scale, of a portion of the oscillator illustrated in Fig. 1 showing the field between the cavity resonator and the repeller electrode and typical electron paths in this field. t Referring now to the drawing, "the electron discharge device illustrated in Fig. 1 comprises an evacuated enclosing vessel having a cupshaped base portion I llprovided with a flange ll and a cup-shaped top portion 12 provided 3 with a flange i3. The portions ill and H may be of metal and are joined hermetically to each other as by Welding the flanges II and I3 together. The base wall of the portion I is pro vided with an aperture in which a vitreous disc I4 is sealed hermetically. Alternatively, the disc 14 may be sealed within the member 4| described hereinafter. plurality of apertures, only one of which is shown, into each of which an eyelet I5 extends, each eyelet being welded hermetically to the flange and having sealed thereto a vitreous bead IS in which a leading-in conductor ll isv sealed.

Mounted within the vessel I0, 12 is. a unitary assembly which comprises an annular foundation plate l8 secured to the flange I 3. as bywelding, and an annular cavity resonator l9 disposed in the opening in the foundation plate I 8 and provided with an annular flange 20 seated on'the plate. The resonant cavity is bounded in part .byfa hollow member having afrusto-conical portion 21 which is. secured to the resonator l9 and is. axially aligned with an aperture 22 in one wall of the resonator, the smaller end of the member 2| and the wall portion in juxtaposition thereto defining a short gap 23. The resonator 5.9. and fru'sto-conical member 2| are fabricated conveniently ofcopper or copper plated steel and the member 21 is joined, as by soldering or welding, to the resonator while. being held in accurate alignment with the aperture 22 by a suitable aligning tool inserted through the aperture 22 andmember 2|.

axially aligned with the. resonator and the gap 23 therein is. an electrode assembly which includes atubular cathode '24 having a dished end portion 25.. provided. with a central aperture, 50 and the concave. surface of which is coated with a ther mionic material, and a tubular beam-forming electrode 26. joined to the cathode and provided with aflange 2?. which extends between a pair oi 'insul'atin'g discs 28, A heater filament 291s supported within thecathode by conductors 3.0 secured to. respective leading-in conductors I l. The cathode, beam-forming electrode 26 and trusto-conical member 2| constitute an axially symmetrical electron gun for producing a concentratedelectron stream converging toward and focused to. a point. upon the. gap 23.

Seated upon the. foundation plate 18 is anarrvru lar metallic. washer 3| upon which there is seated in turn an insulating, for example ceramic, blocl; or plate. 32 having a central aperture 33 in axial alignment with the gap 23. and having also otherapertures 34. The boundingsurface of thecentral aperture 33 is coated with an electrically conductive material, such as silver, to form. .a tubular reflecting electrode 35 to which electrical connection may be established by way of a'leading-in conductor 36 secured thereto and connected to an appropriate leading-in conductor, not shown, extending from the enclosing vessel through an eyelet seal similar to that shown at l5, l6.

Extending through the apertures 34 are. rigid posts. or rods 31 which aresecu-red at one end to the. wall of the resonator I9 opposite the insulating member 132 andare joined at the other end to a rigid bridge piece 38 whichis carried by another rigid post or rod. 39 joined to a sleeve 40 issealed hermetically to the portion t2-of enclosing vessel. The resonator wall mentioned and the base wall of the portion 12 are The flange I3 is provided with a so that the linkage composed of the posts tudinally by suitable means external to the vessel l0, 12 to flex the Wall of the resonator and thus adjust the resonant frequency of the resonant V cavity. Energy may be taken from the cavity by way of a wave guide M, which may be, for example, substantially a narrow rectangle in cross- ..section, secured to the base. wall of the vessel portion H! in alignment with the disc 2H1 and communicating with the cavity through a slit 42 bounded in part by a portion of the resonator l9 and in part by the plate l8. A similar external wave guide 43 may be joined to the base wall of the vessel portion I!) in alignment with the internal guide 4! a In the manufacture of the device, the plate l8, resonator l9 electrode assembly 24, 26, insulating disc 32 and the associated washers 28.and 3| are fabricated as a unitary assembly in which all of the electrodes and the resonator are axially aligned with great accuracy and are firmly maintained in this aligned relation. "Specifically, both the electrodeassernbly 24, 2'6 and the block or disc 32 are positioned in axial alignment with the aperture 22 and member 2! by a suitable aligning tool projecting through the aperture 50, member 21., aperture 22 and repeller electrode 35, and the parts constituting the unitary assembly are clamped firmly together by a plurality of bolts 44,:only one of which is shown. The alignment of the parts after assembly thereof can be checked optically by viewing through theapertures 22 and 50., member 2! and electrode 35.

This assembly, with the tuning linkage in place,

is then mounted upon the vessel portion [,2 by welding the plate l8 to the flange [-3 and the post or rod 39 i sealed to the sleeve 40.. Subsequently, the heater filament 29, is mounted place and the flanges II and l3. are joined hermetically.

The importance of the feature, of the construction which enables fabrication of the electrodes and resonator as a unitary assembly wherein the elements noted are aligned with great. accuracy will be appreciated especially from a consideration of typical-dimensions in a. device of the con struction illustrated in Fig. l and adaptedfor operation at. the order of .1 centimeter wavelength. The. aperture 22 is substantially 0.01 inch in diameter, the repeller electrode is substantially 0.0.6,.inch in internal diameter. and the cathode 24 is substantially 0.125 inch in diameter. Obvious- 1y, a misalignment of eitherthe cathode 25 =or repeller electrode 35 with. thev gap 23..measured in thousandths of an inch will; greatly reduce the operating efliciency and materially affect the operating characteristics of the device inasmuch as. any misalignment reduces either the electron current which is projected into the gap 23,. by the electron gun or the reflected electron current projected into. the gap. 23. from the repeller electrode, or both.

In the operation oi the device, the cavity resonator. I9.- is maintained at a high positive potential. with. respect to the cathode and therepeller electrode. is maintained at a negative potential.

For example in a typical device, the. resonator may be operated at .750 volts positive and-therepell'er-electrode. 1-32 volts negative with respect to the. cathode. Electrons from thecathode are pro.- jected into. the gap 2 3 where they are velocity varied by the field within the resonator and then into the region between the aperture 22 and the .repeller electrode. Here the electrons undergo a drift space. action and reversalin direction of motion and the, v oc ty riations re onverted into density variations. The density varied wide electronic tuning range.

a stream then is projected intothe gap 23 in proper phase to contribute energy to the-fieldwithin the resonator and thus sustain oscillations.

The character of the field in the region in 'which-the drift action occurs is .of prime-importance in the determination of the operating characteristics of the device in that it has an important-effect upon the magnitude of the drift action and the electronic conductance obtained thereby determines the degree of focusing of the reversed electrons upon the gap 23 and also the frequency range throughout which the device can be tuned electronically, i. e., by varying the potential of the repeller electrode 35; The tubular repeller electrode 35 constructed in accordance-with a feature of this invention enables realization, in

"the space in which the drift action occurs, of

fields which result in a high degree of conversion, sharp focusingof the electrons and a-relatively In Fig. 2 the curved numbered lines indicate the equipotential lines in the drift space'in a devicewherein the aperture 22 and repeller electrode 35 are of the dimensions given heretofore, the space between the juxtaposed resonator Wall .and repeller electrode end being substantially electrode constituting-a convergent electron optical mirror. Typical electron trajectories are represented by the lines T. Although, as indicated in the figure, the electron path crosses the axis of the system slightly before, i. e., to the left of, the gap 23, this is not objectionable, but on the contrary is advantageous in that the over convergence compensates for divergence of the electron stream due to space charge, so that a high percentage of the electrons projected into the drift space are returned to the gap 23,

It will be noted further that the field decreases in intensity toward the zero equipotential region. Consequently, a small change in electron energy due to radio frequency voltage across the gap 23 will result in a relatively large change in the distance of travel of an electron from the gap, into the field and back again into the gap and, hence, a correspondingly large change in the transit angle of an electron through the drift space. This results in a wide electron tuning range. Furthermore, a strong drift action is realized and a high negative electron conductance is obtained.

Although a specific embodiment of this invention has been illustrated and described, it will be understood that it is but illustrative and that various modifications may be made therein without departing from the scope and spirit of this invention as defined in the appended claims.

What is claimed is:

1. An electron discharge device comprising an enclosing vessel and a unitary assembly within said vessel, said assembly comprising a foundation member, a cavity resonator having opposed wall portions provided with aligned restricted apertures, an electron gun opposite one of said wall portions and axially aligned with said apertures, a repeller electrode opposite the other of said Wall portions and axially aligned with said apertures, and means separate from said vessel fixedly securing said resonator, gun and repeller electrode to said foundation member.

1 2. An electronrdischarge; device :.-comprisin'g.; an

enclosing vessel and a unitary assemblyiwithin said vessel, said assembly comprising-afoundation member having an aperture therein, a cavity fres'onator within said aperture' andfhaving" 6 posed wallportion's provided with alignedfrestriated" apertures; an electron gun opposit one of said wall portionsandaxially aligned with said restricted apertures, a repeller electrode opposite the other of saidwall portions and axially aligned with said restricted apertures, and means. s'eparate from saidves sel clamping said'member, resonatongun and electrode together.

' 3. An electron" discharge device comprisin-g --a unitary assembly comprising a foundation plate having an aperture'therein, a cavity resonator within. said aperture and having oppos'edwall portions provided with aligned restricted apertures, said resonator having also a flange seated on said plate, a repeller electrode assembly 'opposite one of saidwall portions seated on'said flange and having a hollow conductive portion in alignment with said restricted apertures, an electron gun opposite the other of said wall portions and in alignment with saidrestricte'd'apertures, and means securing said resonator, repeller electrode assembly and gun to said'plate.

'1. Anelectron discharge'device comprisingan enclosing vessel and a unitary assembly within said vessel, said assembly comprising a foundation plate having'an aperture therein, acav'i'ty resonator within said-aperture and having opposed wall portions provided with restricted apertures, a. repeller electrode opposite one of said wall portion and having an opening therein in alignment with said restricted apertures, an electron gun opposite the' other of said wall portions and including a member having an opening therein in alignment with said restricted apertures, and means independent of said vessel seunitary assembly comprising a foundation plate having an aperture therein, a cavity resonator within said aperture and having a supporting portion seated on said plate, said resonator including opposed wall portions provided with aligned restricted apertures, a tubular repeller electrode opposite one of said wall portions and in alignment with said restricted apertures, support means for said repeller electrode, an electron gun opposite the other of said wall portions and including a member having therein an aperture in alignment with said restricted apertures, support means for said gun, and means clamping said supporting portion and said electrode and gun support means to said foundation plate.

6. An electron discharge device comprising a unitary assembly comprising a foundation plate having an aperture therein, a cavity resonator having a flange seated upon one face of said plate and having also opposed wall portions provided with aligned restricted apertures, a tubular repeller electrode opposite one of said wall portions and in alignment with said restricted apertures, support means for said electrode seated upon said flange, an electron gun opposite the other of said wall portions and including a cathode having therein an opening in alignment with said restricted apertures, support means for said gun including a member abutting the other face of said plate, and means clamping said flange and said electrode and :gun support means to satidplate.

,Avelocity variation reflection typ l w --.comprising a. cavity resonator having a gap therev in, means opposite said gap for projecting an .electron'stream thereacross, and means for reversing the 'd'irection'of said stream after it has crossed said gap and again projecting it into said gap, "said second means comprising an open-ended,

- cylindrical 'repelle'r 'electrode defining an electron "optical .mirror having its, focus substantially at said gap.

8. A velocity variation reflection type oscillator comprising a cavity-resonator having opposed wall portions provided with restricted apertures and defining .a gap betweensaid apertures, one of said wall ,portions including a hollow frustoconical member converging toward .said'gap,

"means including said frusto-vconical member and within isaid vessel and having opposed walls "provided with .alignediapertures, oneof said walls being flexible and opposite .said flexible wall por tion, an electron gun opposite one of said walls and in alignment with said apertures, a repeller electrode opposite the otherof said walls and in vali nment with the aperture therein, and rigid means connecting said flexible wall-portion to said flexible wall. 7

10. A velocity variation reflection type oscillator =comprising an enclosing vessel having a flexible Wall position, a unitary'assembly within said vessel including a foundationplate extending substantially parallel to said wall portion, said plate :having an aperture therein, a cavity resonator within {said aperture and having opposed walls provided with aligned apertures and one of which walls is flexible, an "electron-gun opposite one of said walls and in alignment with said aligned apertures, a hollow repeller electrode opposite the other of said walls and in alignment with said aligned apertures, clamping means securing said resonator, gun and repeller electrode to said foundation plate, and means rigidly coupling said flexible wall tosaid wall portion whereby said resonator may be tuned by wall portion. r

JOHN R. PIERCE,

flexure of said 30 Number Name J Date 2,190,511 Cage 1!?6113513,v 1940 2,293,151 Linder Aug. 18, 1942 2250,511 Varianet al. July 29, 1941 v2,220,840

Metcalf Nov. *5, 1940 

